"Possible progress being made in talks with North Korea," Mr Trump wrote in a Twitter post on Tuesday.

"For the first time in many years, a serious effort is being made by all parties concerned. The World is watching and waiting! May be false hope, but the US is ready to go hard in either direction!"

Next month, North Korea and South Korea will have the first meeting between their leaders since 2007 at the border village of Panmunjom, said Chung Eui-yong, head of the South Korean delegation.

Leaders around the world have met the apparent breakthrough with guarded optimism, wary of repeating past negotiations that failed to prevent Pyongyang from developing nuclear weapons and intercontinental ballistic missiles (ICBMs).

Japan's Chief Cabinet Secretary Yoshihide Suga said on Wednesday it was "extremely important" that North Korea show its commitment and concrete actions toward abandonment of its nuclear missile development in a complete, verifiable and irreversible way.

It is believed to be the first time a current US president would meet with the North Korean leader.

In 2009, former President Bill Clinton met with then-leader Kim Jong-il to negotiate the release of two American journalists who had been arrested in North Korea a month earlier.